Confirmed planetTRAPPIST-1 system
TRAPPIST-1 e
A temperate, Earth-sized world near the middle of the habitable zone, often considered the most Earth-like of the seven by size, mass, and heat received.
- Orbital period
- 6.0996 days
- Distance from the star
- 0.0292 AU · 4.37 million km
- Radius
- 0.920 Earth radii
- Mass
- 0.692 Earth masses
- Equilibrium temperature
- About 250 K without an atmosphere
- Rotation
- Likely tidally locked
- Discovery
- 2017 · transit
- Host star
- M8V ultracool dwarf · about 0.09 solar masses
- Distance from the Sun
- 40.7 light-years
The most Earth-like of the seven
TRAPPIST-1 e orbits in the middle of the star's habitable zone and receives roughly two-thirds of the solar energy Earth receives. Its equilibrium temperature is around 250 K, and a modest greenhouse effect could warm its surface to conditions where liquid water is possible.
At 0.92 Earth radii and 0.69 Earth masses, its bulk density is close to Earth's. That makes e a natural benchmark: the planet in this system most similar to our own in size, mass, and the amount of starlight it receives.
A possible ocean world, unproven
Some models suggest e could hold a substantial water fraction, perhaps enough for a deep global ocean beneath a modest atmosphere. Others find it could be a dry, rocky world. The difference hinges on the planet's exact density and how much water it retained during formation.
None of this has been observed directly. The "ocean world" description is a plausible model, not a measurement. No atmosphere has been detected, and the planet's actual surface is completely unknown.
What we don't know
Future observations will try to detect an atmosphere and, if one exists, measure its composition. Because the star is faint and the planet small, these measurements are at the edge of current capability and will improve with the next generation of telescopes.
- Does it have an atmosphere, and of what kind?
- Is it an ocean world, a desert world, or something in between?
- Could any of its water remain liquid on the surface?
Key publications
| Year | Paper | Venue | Link |
|---|---|---|---|
| 2017 | Gillon et al., Seven temperate terrestrial planets around TRAPPIST-1 | Nature 542, 456 | DOI |
| 2021 | Agol et al., Refined masses, radii, and densities of the TRAPPIST-1 planets | Planetary Science Journal 2, 1 | DOI |
Values compiled from the NASA Exoplanet Archive and the papers listed above.
Worth knowing
It is often called the most Earth-like of the seven.
It sits in the middle of the habitable zone.
Its year lasts about 6 Earth days.